U.S. patent application number 11/196634 was filed with the patent office on 2006-03-16 for chemical microreactor and method thereof.
This patent application is currently assigned to The Regents of the University of California. Invention is credited to Alan Jankowski, Jeffrey D. Morse.
Application Number | 20060057039 11/196634 |
Document ID | / |
Family ID | 21725998 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060057039 |
Kind Code |
A1 |
Morse; Jeffrey D. ; et
al. |
March 16, 2006 |
Chemical microreactor and method thereof
Abstract
Disclosed is a chemical microreactor that provides a means to
generate hydrogen fuel from liquid sources such as ammonia,
methanol, and butane through steam reforming processes when mixed
with an appropriate amount of water. The microreactor contains
capillary microchannels with integrated resistive heaters to
facilitate the occurrence of catalytic steam reforming reactions.
Two distinct embodiment styles are discussed. One embodiment style
employs a packed catalyst capillary microchannel and at least one
porous membrane. Another embodiment style employs a porous membrane
with a large surface area or a porous membrane support structure
containing a plurality of porous membranes having a large surface
area in the aggregate, i.e., greater than about 1 m.sup.2/cm.sup.3.
Various methods to form packed catalyst capillary microchannels,
porous membranes and porous membrane support structures are also
disclosed.
Inventors: |
Morse; Jeffrey D.;
(Martinez, CA) ; Jankowski; Alan; (Livermore,
CA) |
Correspondence
Address: |
Lawrence Livermore National Laboratory
P.O. Box 808, K-703
Livermore
CA
94551
US
|
Assignee: |
The Regents of the University of
California
|
Family ID: |
21725998 |
Appl. No.: |
11/196634 |
Filed: |
August 2, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10007412 |
Dec 5, 2001 |
6960235 |
|
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11196634 |
Aug 2, 2005 |
|
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Current U.S.
Class: |
422/198 |
Current CPC
Class: |
B01J 2219/00873
20130101; B01J 19/0093 20130101; B01J 2219/00828 20130101; B01J
2219/00783 20130101; B01J 2219/00844 20130101; B01J 2219/00835
20130101; B01J 2219/00831 20130101; B01J 2219/00871 20130101; B01J
2219/00824 20130101 |
Class at
Publication: |
422/198 |
International
Class: |
B01J 19/24 20060101
B01J019/24; B81B 1/00 20060101 B81B001/00 |
Goverment Interests
[0002] The United States Government has rights in this invention
pursuant to Contract No. W-7405-ENG-48 between the United States
Department of Energy and The University of California for the
operation of Lawrence Livermore National Laboratory.
Claims
1. A method for forming a chemical microreactor comprising: forming
at least one capillary microchannel within a substrate having at
least one inlet and at least one outlet, forming at least one
porous membrane, imbedding the porous membrane with at least one
catalyst material, integrating at least one heater into the
chemical microreactor, interfacing the capillary microchannel with
a liquid chemical reservoir at the inlet of the capillary
microchannel, interfacing the capillary microchannel with the
porous membrane at the outlet of the capillary microchannel, such
that gas flow moves in a horizontal direction from the inlet
through the microchannel and moves in a vertical direction from the
microchannel through the outlet.
2. The method of claim 1, additionally including forming the porous
membrane using at least one of the techniques selected from the
group consisting of thin film deposition, thick film formation,
electrochemical etching, plasma etching and selective chemical
etching.
3. The method of claim 1, additionally including imbedding the
catalyst material within the porous membrane by a thin film
deposition technique.
4. The method of claim 1, additionally including imbedding the
catalyst material by ion exchange.
5. The method of claim 1, additionally including imbedding the
catalyst material by solgel doping.
6. The method of claim 1 producing a chemical microreactor
comprising: a plurality of separate reaction microchannels within a
silicon substrate, each reaction microchannel within a silicon
substrate, each reaction microchannel having at least one inlet and
at least one outlet, at least one of the reaction microchannels
comprising a steam reformer for a hydrogen-containing fuel having a
reforming catalyst material between the at least one inlet and the
at least one outlet, and at least one other of the reaction
microchannels comprising an integrated catalytic microcombustion
heater having at least one heater catalyst material between the at
least one inlet and the at least one outlet, wherein at least one
of the at least one inlet and the at least one outlet for each of
the plurality of separate reaction microchannels is an additional
non-reaction microchannel oriented non-parallel to the
corresponding reaction microchannel, whereby a fully integrated
silicon chemically heated steam reforming microreactor that
maintains gas separation between the reformer and heater
microchannels is provided.
7. The method of claim 6 further comprising: at least one porous
membrane located between said reformer inlet and said outlet.
8. The method of claim 6 wherein said catalyst material is selected
from the group consisting of platinum, platinum-ruthenium, nickel,
palladium, copper, copper oxide, ceria, zinc oxide, alumina,
combinations thereof and alloys thereof.
9. The method of claim 6, wherein the said reformer outlet connects
to a manifold of a fuel cell.
10. The method of claim 6, wherein said at least one catalyst
material located between said inlet and said outlet is packed into
said reformer microchannel.
11. The method of claim 7, wherein said at least one catalyst
material located between said inlet and said outlet are imbedded in
said porous membrane in said reformer microchannel.
12. The method of claim 6, wherein said reformer microchannel inlet
connects to a liquid fuel reservoir.
13. The method of claim 7, wherein said reformer microchannel is
interfaced with said porous membrane such that fuel flow moves in a
horizontal direction from said reformer microchannel inlet through
said reformer microchannel and moves in a vertical direction from
said reformer microchannel through said reformer microchannel
outlet.
14. The method of claim 6, wherein said heater is integrated at
said inlet.
15. The method of claim 6, wherein said heater is integrated along
said reformer microchannel.
16. The method of claim 7, wherein said heater is integrated at
said porous membrane.
17. The method of claim 7, wherein said porous membrane comprises a
porous thick film selected from the group consisting of porous
silicon, anodic alumina, zerogel, glass and combinations
thereof.
18. The method of claim 7, wherein the catalyst material covers a
surface area of the porous membrane measuring about 1
m.sup.2/cm.sup.3 or greater.
19. The method of claim 6, wherein the microchannels support a fuel
flow rate in the range of about 1 microliter/minute to about 600
microliters/minute.
20. The method of claim 7, further comprising: a porous getter
structure located at the exit side of said porous membrane.
21. The method of claim 20, wherein the surface area and volume of
the getter structure is about 1 m.sup.2/cm.sup.3 or greater.
22. The method of claim 6, wherein said microreactor is configured
to process more than one type of liquid fuel component into
hydrogen fuel.
Description
RELATED APPLICATION
[0001] This application is a Divisional of U.S. patent application
Ser. No. 10/007,412 filed Dec. 5, 2001 and claims priority
thereof.
BACKGROUND OF THE INVENTION
[0003] Porous membrane reactors typically utilize a bulk porous
media which is affixed to the end of stainless steel tubing through
which the chemical species is delivered. For the application of
steam reforming hydrogen containing fuels, a catalyst is introduced
to the porous membrane and the entire fixture is heated as gas is
delivered to the membrane. While steam reforming of methanol has
been reported at 350.degree. C., typical operating temperatures are
high, e.g., 500.degree. C. to 700.degree. C. due to the inability
of the reactor to adequately exchange heat with the outside
environment.
[0004] German patent application, DE 1998-19825102 discloses a
method to produce catalytic microreactors that includes "placing a
catalyst in the reaction spaces." The microreactors can be used for
steam reforming or partial oxidation of hydrocarbons to produce
hydrogen gas for fuel cells.
[0005] Srinivasan et al disclose in the American Institute of
Chemical Engineers (AIChE) Journal (1997), 43(11), 3059-3069, a
silicon-based microfabrication of a chemical reactor (microreactor)
having submillimeter flow channels with integrated heaters, and
flow and temperature sensors. The article discusses the potential
applications of this reactor and the feasibility of a variety of
operating conditions.
SUMMARY OF THE INVENTION
[0006] Aspects of the invention include a microreactor comprising:
at least one etched microchannel structure within a substrate
having at least one inlet and at least one outlet, at least one
integrated heater, and at least one catalyst material between the
inlet and the outlet.
[0007] Another aspect of the invention includes a microreactor
comprising: a top substrate and a bottom substrate such that at
least one capillary microchannel is contained between the top
substrate and the bottom substrate, the capillary microchannel
having at least one inlet and at least one outlet, a plurality of
catalyst materials located between the inlet and the outlet, at
least one porous membrane located at the outlet, and at least one
integrated heater.
[0008] Another aspect of the invention includes a method for
forming a chemical microreactor comprising: forming at least one
capillary microchannel within a substrate having at least one inlet
and at least one outlet, forming at least one porous membrane,
imbedding the porous membrane with at least one catalyst material,
integrating at least one heater into the chemical microreactor,
[0009] Interfacing the capillary microchannel with a liquid
chemical reservoir at the inlet of the capillary microchannel,
interfacing the capillary microchannel with the porous membrane at
the outlet of the capillary microchannel, such that gas flow moves
in a horizontal direction from the inlet through the microchannel
and moves in a vertical direction from the microchannel through the
outlet.
[0010] Another aspect of the invention includes a method of
operating a chemical microreactor comprising: delivering a fuel
source from an inlet through a microfluidic capillary that is
packed with a catalyst material to a porous membrane, heating the
microfluidic capillary and the porous membrane to a temperature
between about 250.degree. C. and about 650.degree. C., and
reforming the fuel source into hydrogen and a plurality of other
gaseous materials while simultaneously passing at least the
hydrogen through the porous membrane into at least one gas flow
channel that is connected to at least one fuel cell.
[0011] Another aspect of the invention includes a method of
operating a chemical microreactor comprising: delivering a fuel
source through a first microfluidic capillary to a porous membrane
that is imbedded with a catalyst material, heating the microfluidic
capillary and the porous membrane to a temperature between about
250.degree. C. and about 650.degree. C., and reforming the fuel
source into hydrogen and a plurality of other gaseous materials
while simultaneously passing at least the hydrogen through the
porous membrane into at least one gas flow channel that is
connected to at least one fuel cell.
[0012] Another aspect of the invention includes a method
comprising: providing means for generating a hydrogen fuel from a
liquid source, and delivering the hydrogen fuel to a fuel cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A shows an embodiment of a microreactor.
[0014] FIG. 1B shows a top view of the porous membrane structure
portion of an embodiment of a microchannel.
[0015] FIG. 2A shows a cross-sectional view of an embodiment of a
microreactor with multiple microchannels.
[0016] FIG. 2B shows a cross-sectional view of the microchannel and
resistive heater portion of an embodiment of a microreactor.
[0017] FIG. 3 shows a cross-sectional view of the microchannel and
resistive heater portion of an embodiment of a microreactor with
multiple microchannels.
[0018] FIG. 4A shows a cross-sectional view of the microchannel and
resistive heater portion of an embodiment of a microreactor.
[0019] FIG. 4B shows a cross-sectional view of the microchannel and
resistive heater portion of an embodiment of a microreactor with
multiple microchannels.
[0020] FIG. 5 shows a cross-sectional view of an embodiment of a
microreactor integrated with a microcumbuster.
DETAILED DESCRIPTION
[0021] Referring to FIG. 1A, a chemical microreactor 2 comprises: a
bottom substrate 4a comprising silicon, glass or ceramic, a top
substrate 4b comprising silicon, glass or ceramic, at least one
capillary microchannel 6 having at least one inlet 8 for fuel and
water and at least one outlet 10 for gases, a liquid reservoir (not
shown) containing a fuel source, at least one porous membrane 12,
and at least one integrated heater 14 for heating the microchannel.
Referring to FIG. 1B, a porous membrane support structure 13
comprising silicon, glass or ceramic containing a plurality of
porous membranes 12 is an effective alternate embodiment to porous
membrane 12 of FIG. 1A. Microreactor 2 can further comprise a
catalytic combustion microfluidic heat source (not shown) to heat
the gases flowing through the microchannel and porous
membrane(s).
[0022] Chemical microreactor 2 provides a means to generate
hydrogen fuel from liquid sources such as ammonia, methanol, and
butane through steam reforming processes when mixed with the
appropriate amount of water. In an alternate embodiment to that
shown in FIG. 1A, capillary microchannel inlet 8 mixes and delivers
a fuel-water mixture from the liquid reservoir (not shown) through
microchannel 6 and porous membrane 12. Porous membrane 12 can
alternately be replaced with a porous membrane support structure
containing a plurality of porous membranes.
[0023] Referring to FIG. 2A, the fuel-water mixture can first be
heated by resistive heaters in a "gassifier region" 15, i.e., the
region where the fuel inlet connects to the microchannel, forming a
fuel-steam gas. The fuel-steam gas then flows through microchannel
6. The microchannel can be packed with a catalyst material such as,
platinum, platinum-ruthenium, nickel, palladium, copper, copper
oxide, ceria, zinc oxide, alumina, combinations thereof and alloys
thereof. Resistive heaters 14 can be positioned along the
microchannel. Heating microchannel 6 to a temperature between about
250.degree. C. and about 650.degree. C. by resistive heaters
facilitates the occurrence of catalytic steam reforming reactions.
The desired temperature depends upon the source of fuel. For
example, about 250.degree. C. is an effective temperature if
methanol is used, whereas ammonia requires a temperature closer to
about 650.degree. C. Microchannel 6 is formed in a configuration
that allows adequate volume and surface area for the fuel-steam gas
to react as it flows through microchannel 6 and porous membrane 12.
Electrical connection pads 16 provide current to resistive heaters
14. Although not shown, electrical pads 16 are connected to a power
source. FIG. 2B is a cross-sectional illustration of the embodiment
depicted in FIG. 2A.
[0024] Two distinct embodiment styles are effective. The first
embodiment employs a packed catalyst capillary microchannel and at
least one porous membrane. In this embodiment, the primary purpose
of the porous membrane is to prevent large particles or molecules
flowing through the microchannel to pass through the membrane. The
porous membrane may or may not contain catalyst materials.
[0025] The second embodiment style employs a porous membrane with a
large surface area or a porous membrane support structure
containing a plurality of porous membranes having a large surface
area in the aggregate, i.e., greater than about 1 m.sup.2/cm.sup.3.
Surface areas on the order of about 1 m.sup.2/cm.sup.3 to about 100
m.sup.2/cm.sup.3 are effective. In this embodiment, a catalyst
material is imbedded within the porous membrane(s) and the primary
purpose of the porous membrane(s) is to facilitate the occurrence
of catalytic steam reforming reactions. Packed catalyst capillary
microchannels may or may not be used with this embodiment style.
This embodiment style can reduce the size and length requirements
of microchannel 6. For example, referring to FIGS. 1A and 1B,
positioning porous membrane support structure 13 which contains a
plurality of porous membranes 12 at outlet 10 of microchannel 6
provides a high surface area catalytic reaction. Minimizing the
size of the microchannel region in this manner makes it easier to
heat and maintain microchannel 6 at the high temperatures required
for the steam reforming reactions to occur, i.e., about 250.degree.
C. to about 650.degree. C. Additionally, the porous membrane
support structure 13 provides a flow interface with outlet 10 and
provides some restriction to gas flow resulting in a slight
increase in the back-pressure of the microchannel region.
[0026] Hydrogen gas is generated by heating microchannel 6 and
porous membrane 12 to an appropriate temperature, i.e., about
250.degree. C. to about 650.degree. C. The fuel-steam source is
reformed into gaseous byproducts, i.e., hydrogen and subsequent
byproducts, such as carbon monoxide and carbon dioxide, as the
molecules diffuse through the membrane and flow into a fuel cell or
other power source. Hydrogen is the component of the liquid fuel
source that is converted into energy by a fuel cell. If chemical
microreactor 2 is used in concert with a fuel cell, the gaseous
molecules, after passing through the membrane structure, flow
through at least one other microchannel, i.e., a gas flow channel.
The gas flow channel is located at the exit side of catalytic
membrane 12 and is connected to the anode manifold of a fuel cell.
Additional embodiments can include the integration of a porous
getter structure or permaselective membrane material at the exit
side of porous membrane 12 to adsorb the product gases allowing
only the hydrogen to diffuse through to the fuel cell. It is
beneficial to adsorb product gases if the presence of the
additional byproducts will degrade the components of the fuel cell.
Any fuel cell that uses hydrogen as a fuel source can be
effectively used with this invention. For example, effective fuel
cells include the micro-electro mechanical system based
(MEMS-based) fuel cells discussed in U.S. patent application Ser.
No. 09/241,159 by Alan Jankowski and Jeffrey Morse which is hereby
incorporated by reference.
[0027] A chemical microreactor can be constructed by using
micromachining of silicon, glass, or ceramic materials, and wafer
bonding. This method of construction involves first forming the
microchannel by etching a pattern in the bottom surface of a
substrate. For example, the pattern may be serpentine or straight.
The depth of the microchannel is approximately 200 .mu.m, and
penetrates only a fraction of the way through the total depth of
the substrate, which can range in thickness from about 400 .mu.m to
about 600 .mu.m. Referring to FIGS. 2A (top view) and 2B
(cross-sectional view), resistive heaters 14 are formed on the top
surface of substrate 4b and positioned above microchannel 6 in a
manner which optimizes the heat transfer from the heaters to the
microchannels. The resistive heaters can also be formed on the top
surface of substrate 4a, so that they are positioned adjacent to
the surface of the microchannel. Thus, the power input required to
heat the fuel-water to product gases and complete the catalytic
reaction as the gases flow through the channel is minimized.
[0028] Further embodiments facilitate a process referred to as
counter-flow heat exchange. Such embodiments position the
microchannels in configurations that permit the heat that is lost
from the product gases flowing through one microchannel to be
transferred to gas flow streams in adjacent microchannels. Such
embodiments can include counterflow heat exchangers (not shown).
The counterflow heat exchangers can be located in the following
three areas and serve three different functions. First, counterflow
heat exchangers can be located in the gassifier region to initially
heat the fuel water mixture. A second set of counterflow heat
exchangers can be located in the area between the gassifier region
and the packed catalyst microchannel to add extra heat to the gas
as it flows into the capillary microchannel. Finally, more
counterflow heat exchangers can be located at the outlet of the
porous membrane to recuperate any extra heat given off by the
byproduct flow stream. The hot gas outlet of catalytic
microreactors integrated with a fuel cell connect directly to the
fuel cell anode manifold, and incorporate a counterflow heat
exchanger at the fuel cell anode exhaust. That counterflow heat
exchanger transfers extra heat from the anode exhaust from the fuel
cell back through the gassifier region and inlet flow stream to the
catalytic microreactor.
[0029] The inlet port(s) 8 and porous membrane structure 13 are
formed by patterning and etching into the top surface of the
substrate 4a. Referring to FIG. 3, an inlet port 8 is approximately
1 mm in diameter and opens up to the entrance of microchannel 6.
Separate inlets for fuel and water may be formed, or a single inlet
for premixed fuel-water mixtures (as shown in FIG. 3) may suffice.
An array of vias 17 with diameters ranging from 0.1-5.0 .mu.m can
be patterned and etched into a porous membrane support structure
13. The pores are straight, and go through to the end of
microchannel 6 (for example, about 100 .mu.m to about 200 .mu.m
deep). Silicon can be etched using conventional plasma etch (Bosch
process) techniques, laser etching, or photoinduced electrochemical
etching. Each etching technique will create an array of very
straight, deep, narrow pores which extend to the microchannel,
which is formed from the bottom side.
[0030] Another approach to forming a porous silicon membrane is to
use an electrochemical etch technique whereby hydrofluoric acid is
used to etch pores in the silicon. The electrochemical etch creates
a random porous layer in the silicon. The pore sizes, for example,
have diameters of about 0.1 .mu.m to about 1.0 .mu.m, and
thicknesses on the order of about 60 .mu.m to about 200 .mu.m.
[0031] A porous membrane support structure can be positioned at the
outlet of the microchannel using a combination of thin film
deposition, thick film formation, and electrochemistry techniques.
Referring to FIG. 4A, the membrane structure 13 may be a porous
thick film structure comprising anodic alumina, xerogel, or glass
and is formed over an opening creating vias 17 which are etched
down to the microchannel 6 at the outlet end. FIG. 4B shows a
multiple channel embodiment. In one example, a thick film membrane
comprising xerogels is formed by depositing a solgel coating of
glass on the top surface of the substrate, and drying it in such a
way as to create random porosity through the film. For instance, a
30 minute bake at 120.degree. C. to remove any remaining solvents
is followed by a high temperature bake at 600-800.degree. C. Others
methods known to those familiar with the art will also apply. The
diameter of these pores may range in size from about 0.1 .mu.m to
about 1.0 .mu.m, and the film can be up to about 100 .mu.m
thick.
[0032] In a second example, the membrane 13 is formed by bonding a
porous alumina film about 50 .mu.m thick to the top surface of the
substrate 4a over an opening leading to the microchannel 6. The
porous alumina is formed by anodization of aluminum which creates
arrays of narrow pores ranging in diameter from about 0.02 .mu.m to
about 0.2 .mu.m.
[0033] The porous thick film membrane structure has two primary
purposes. First, it provides mechanical strength in the case where
a pressure differential exists between the inlet 8 to microchannel
and the outlet 10 from the microchannel. Second, it provides a
natural flow control of the gaseous reaction byproducts flowing
through the porous membrane 12. The membrane structure can be
controlled for the specific requirements of the power source it is
feeding. For example, the fuel, when fully processed, in a 6
microliters/minute flow of a methanol:water (50:50) fuel mixture
can provide approximately 500 milliwatts of electrical power from a
fuel cell at 50 percent efficiency if the microchannels and
microfluidic system are designed to provide minimal pressure drops
the 6 microliters/minute flow rate.
[0034] Once the microchannels, porous membrane structures,
resistive heaters, and counterflow heat exchangers are formed, the
catalytic microreactor is completed by integrating the catalyst
materials into the microchannel and porous membrane, then bonding a
first substrate 4a made of glass, silicon, or ceramic to a second
substrate 4b made of glass, silicon, or ceramic.
[0035] The catalyst used may be platinum, platinum-ruthenium,
nickel, palladium, copper, copper oxide, ceria, zinc oxide,
alumina, combinations thereof, alloys thereof or other materials
commonly used in steam reforming processes. Various coating methods
are used to position the catalyst materials. For example, the
catalyst materials can be imbedded within the membrane and the
microchannel by thin film deposition techniques or they can be
imbedded within the microchannel and porous membrane structure by
ion exchange or solgel doping methods. These coating methods can be
tailored to provide porous, high surface area coatings, thereby
enhancing the reaction kinetics.
[0036] Other effective processes use small pellets or particles of
a supported catalyst material, such as Copper/Zinc Oxide/Alumina,
for example, which are larger in diameter than the pore sizes of
the porous membrane. This kind of catalyst material is commercially
available, and is typically formed by imbedding the copper/zinc
oxide materials in to a porous alumina support particle. Once
formed, the catalyst particles can be colloidally suspended in a
liquid solution. The colloidal solution can then be injected
through the microchannel. The porous membrane traps the catalyst
particles inside the microchannel. After some time, the
microchannel becomes filled with catalyst particles. This process
creates a packed catalyst microchannel that is porous enough for
gases to readily flow through and at the same time be exposed to a
high surface area of catalyst materials. This process can be used
in combination with the catalyst coating methods described above,
or by itself.
[0037] The membrane area and microchannel areas are made large
enough to allow sufficient fuel flow for the power source
requirements. In some cases, if resistive heaters require too much
input electrical power to heat the microchannels and porous
membrane, exothermic combustion reactions may be initiated. These
exothermic combustion reactions may be self-sustaining and thus, do
not require additional power.
[0038] Referring to FIG. 5, these self-sustaining exothermic
combustion reactions can be accomplished by forming a
microcombustor 20. Microcombuster 20 comprises a small microchannel
22 with a catalyst wire or electrode 23 (typically is a catalyst
bed heater), which is separate from the capillary microchannel 6
and porous membrane 12, and at least one electrical contact pad 30
connected to a power source (not shown). This microcombustor has a
first inlet 24 for a fuel such as butane or methanol, which is
heated with a small resistive heater to form a gas, and a second
inlet 26 for air or other oxygen-containing gaseous mixture. The
fuel and air are mixed and flow over the catalyst wire or
electrode, which is heated by running a current through it similar
to a resistor. The fuel/air mixture then ignites a combustion
reaction which generates heat, carbon dioxide and water. The heat
is transferred to the capillary microchannel and porous membrane
and the carbon dioxide and water flow to an outlet (not shown).
Once ignited, the reaction is sustained as long as fuel and air
flow through inlets 24 and 26 without further current flowing
through the catalyst wire 23 or filament. The heat generated from
the combustion reaction can be efficiently transferred to the
chemical microreactor and, if present, an integrated fuel cell,
using the counterflow heat exchange process described above. The
outlet gas stream from the microchannel combustor will be hot, and
this heat can be readily transferred through high surface area
microchannels to adjacent cold gases flowing in opposite
directions. The microchannel combustor can be formed using the same
approaches described above for the chemical microreactor. In
certain fuel cell embodiments, heat may be coupled between the
steam reforming packed catalyst microchannel and porous membrane
and the fuel cell, thereby reducing the power requirement to heat
the fuel cell and make a very efficient power source. The membrane
material and porosity, catalyst deposition, and integrated heater
layout can be optimized to match a specific fuel, such as methanol,
or specific groups of fuels, such as ammonia, methanol and
butane.
[0039] Several microreactors can be integrated to allow processing
of a variety of liquid fuel components. Integrated microreactors
which incorporate both fuel cells and fuel reforming may be
fabricated in parallel in order to make them suitable for higher
power applications ranging from about 10 Watts to about 50
Watts.
[0040] While particular operational sequences, materials,
temperatures, parameters, and particular embodiments have been
described and or illustrated, such are not intended to be limiting.
Modifications and changes may become apparent to those skilled in
the art, and it is intended that the invention be limited only by
the scope of the appended claims.
* * * * *